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WAEC Mathematics 2013 Paper

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Question : 5

Total: 48

If Un = n(n² + 1), evaluate U5 - U4

18
56
62
80

Solution:

Concept:

Substitute

n = 5

and

n = 4

into the given formula

U_n = n(n^2 + 1)

to find the required difference.

Explanation:

Find

U_5

by putting

n = 5

:

U_5 = 5(5^2 + 1)

= 5(25 + 1)

= 5(26) = 130

Find

U_4

by putting

n = 4

:

U_4 = 4(4^2 + 1)

= 4(16 + 1)

= 4(17) = 68

Now subtract:

U_5 - U_4 = 130 - 68 = 62

Answer:

62

, so the correct option is C.

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